Method and apparatus for noninvasive determination of cardiac performance parameters

ABSTRACT

Apparatus and method for noninvasively determining cardiac performance parameters including 1) lengths of systolic time intervals, (2) contractility index, (3) pulse amplitude ratios while performing the Valsalva maneuver, (4) cardiac output index, and (5) a pulse wave velocity index. A catheter having at least one balloon is inserted into the esophagus and pressurized and positioned adjacent the aortic arch to sense aortic pressure. The effects of aortic pressure on the balloon are utilized to determine at least one of the cardiac performance parameters. The catheter may include a second balloon which is spaced from the aortic balloon a distance such that when the second balloon is in a position adjacent the left atrium to sense left atrial pressure the aortic balloon is in a position adjacent the aortic arch to sense aortic pressure, this distance being related to the distance between the left atrium and aortic arch in most adult persons.

Priority of co-pending U.S. provisional patent application Ser. No.60/049,459, filed Jun. 12, 1997, is hereby claimed. This provisionalapplication is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to an apparatus and method fornoninvasive monitoring of one or more cardiac performance parameters,and more particularly to a method and an apparatus which includes acatheter which may be positioned in the esophagus and associatedapparatus for monitoring cardiac performance.

BACKGROUND OF THE INVENTION

The diagnosis and care of patients with cardiovascular diseasecritically depends on information about the pumping ability of theheart. For example, the priming pressure of the left ventricle of theheart, typically obtained by measurement of left atrial pressure,indicates, when abnormal, a mismatch between volume capacity of thevascular system and the circulatory blood volume.

Since the early 1970's, the flow-directed pulmonary artery ballooncatheter (a.k.a. the Swan-Ganz catheter) has been the standard forbedside hemodynamic monitoring. It yields cardiac output bythermodilution as well as an estimate of mean left atrial pressure.However, under certain conditions, the pressure readings may notfaithfully reflect left atrial pressure (R. RAPER et al, "Misled by theWedge", Chest, March 1986, pp. 427-434). This invasive technique ispersonnel intensive and costly since the catheter must be inserted andused in a critical care area or operating room, and it has beenassociated with infection, arrhythmias, and death (E. ROBIN et al, "TheCult of the Swan-Ganz Catheter", Annals of Internal Medicine, September1985, vol. 103, pp. 445-449). Its use is further limited since it onlyprovides non-automated intermittent measurements, and the cathetershould, for safety reasons, only be left in the patient for a few days.

My U.S. Pat. Nos. 5,048,532; 5,181,517; 5,263,485; 5,398,692; 5,551,439;5,570,671; and 5,697,375, all of which patents are incorporated hereinby reference, disclose noninvasive methods and apparatus which includesa catheter containing an inflatable balloon insertable into theesophagus for placement adjacent the left atrium, and associatedequipment for making determinations of mean left atrial and mean leftatrial transmural pressures. A second catheter containing a secondballoon may be used therewith for determining esophageal pressure, whichis then added to the mean left atrial transmural pressure to obtain adetermination of mean left atrial pressure. Alternatively, a singleballoon is used for both purposes wherein the single balloon is moved upthe esophagus to measure esophageal pressure and then moved back to theleft atrial position. The catheter may also include an esophagealstethoscope and/or an esophageal temperature sensor contained within aprotective pouch which surrounds the catheter.

In accordance with one method of positioning the balloon as discussed inmy aforesaid U.S. Pat. No. 5,570,671, an electrode means is attached tothe catheter just above the balloon to obtain a cardiogram at each of aseries of incremental depths as the electrode is moved lengthwise withinthe esophagus, the esophageal depth at which the balloon is positionedbeing that which corresponds to the incremental electrode depth at whichthe electrogram therefor shows the greatest negative portion length ofthe largest absolute value segment of the respective "p" wave.

However, suitably monitoring a patient's heart condition requires, ofcourse, more than determining the mean left atrial and mean left atrialtransmural pressures. Impedance cardiography, which depends on attachinga number of electrodes to the chest, yields continuous readouts ofcardiac output, the blood flow generated by the heart. Many researchersconsider that this method is unreliable for absolute values but good forrelative changes. This device can also provide systolic time intervals.The systolic time interval includes the duration of two phases ofventricular activity: the pre-ejection period (PEP) and the leftventricular ejection time (LVET); PEP refers to the time spent by theventricle increasing pressure on the volume of blood in it beforeejection of the blood into the aorta, and LVET is the duration of theejection phase. These time intervals are used in various combinations togauge ventricular performance. For instance, a long PEP is seen when theheart is pumping against increased resistance. Also, the ratio PEP/LVETis known to decrease as cardiac output increases. However, thisimpedance cardiography method is unable to measure pressures or assessvalvular function and furthermore does not work well on the criticallyill.

Electrocardiographic analysis of the heart's beating frequency andrhythm allows conclusions about the efficiency of the pump (heart). Forinstance, an abnormally high beating frequency will preclude effectivepriming of the pump. In addition, the chambers of the heart must act insynchrony for efficient pumping and, for instance, atrial fibrillationwill degrade cardiac output.

Transthoracic and transesophageal echocardiography are excellenttechniques for evaluation of valvular function of the heart with respectto leakage and resistance to flow and ventricular pumping action andsystolic time intervals. However, the equipment is expensive, the methodis very personnel intensive, and the esophageal probe, being large indiameter (perhaps about 9 or 10 mm) is uncomfortable and requiressedation of the patient. This technique also does not lend itself tocontinuous unattended monitoring of the patient.

Esophageal ultrasound Doppler flow-probe technique provides a goodanalysis of flow velocity in the descending aorta but gives only partialinformation about cardiac function. This technique also requires atrained operator. Although it can provide continuous monitoring, smallposition changes in the probe may make readings unreliable.

Phonocardiography is carried out by placing one or more microphones onthe patient's chest. It can give a good analysis of valvular function,but it is susceptible to interference by extraneous sound sources.

Carotid plethysmography offers a qualitative representation of thecarotid artery pulse and is used in combination with electrocardiographyand phonocardiography to produce systolic time intervals. The method is,however, personnel intensive and not useful for continuous monitoring.

U.S. Pat. Nos. 4,094,308 and 5,086,776 suggest noninvasive methods forsensing cardiac performance. However, these methods are not sufficientlyreliable and/or are personnel intensive and/or do not suitably allowcontinuous automated monitoring of the patient.

The combination of a sphygmomanometer (the common blood pressure cuff),a Swan-Ganz catheter, a phonocardiograph, a carotid plethysmograph, andan electrocardiograph has provided a comprehensive evaluation of cardiaccontractility. See "An Indirect Method of Evaluation of Left VentricularFunction in Acute Myocardial Infarction" by C. Agress et al,Circulation, vol. XLVI, August 1972, pp. 291-297. The maximum rate ofleft ventricular pressure change as a function of left ventricular enddiastolic pressure (which equals mean left atrial pressure) has beenused to determine cardiac pumping function in patients with myocardialinfarction and acute coronary insufficiency with marked predictive valuefor survivors and non-survivors. Unfortunately, this invasive methodsuffers from being complicated and cumbersome and carries the risksinherent in cardiac catheterization.

OBJECTS AND SUMMARY OF THE INVENTION

It is accordingly a principal object of the present invention tononinvasively determine cardiac performance parameters on a real timebasis using novel apparatus and measuring techniques.

More specifically, it is an object of this invention to noninvasivelyand reliably determine mean left atrial and mean left atrial transmuralpressures.

It is a further object of this invention to noninvasively measuresystolic time intervals.

It is a still further object of this invention to noninvasively obtain acontractility index (dp/dt/MLAP).

It is a further object of this invention to noninvasively obtain ameasure of pulse amplitude ratios while performing the Valsalvamaneuver.

It is a further object of the present invention to noninvasively obtainan index of cardiac output.

It is a further object of this invention to noninvasively measure pulsewave velocity.

It is another object of the present invention to provide apparatustherefor which is reliable, inexpensive, easy to use, allows continuousautomated monitoring of the patient, and can be employed by paramedicalpersonnel with minimal training.

In order to noninvasively obtain at least one cardiac performanceparameter, in accordance with the present invention, a catheterincluding at least one inflatable balloon is provided for insertion intothe esophagus, means is provided for pressurizing the balloon, and meansis provided for positioning the balloon to sense aortic pressure on theballoon so that, with use of associated apparatus, at least one cardiacperformance parameter may be obtained.

In order to provide a single noninvasive instrument for obtaininginformation regarding both left atrial and aortic pressures fordetermining cardiac performance parameters, in accordance with thepresent invention, a catheter, with which an ECG and an automatic bloodpressure cuff or other suitable means for measuring blood pressure andother associated apparatus may be used, is provided which is insertableinto the esophagus and which includes at least two inflatable balloons.Means is provided for pressurizing the balloons. The balloons are spacedapart so that when one balloon is positioned adjacent the left atriumthe other balloon is positioned adjacent the aortic arch. Meansutilizing effects of left atrial and aortic pressures on the respectiveinflated balloons is provided for obtaining determinations of as well ascontinuously monitoring cardiac performance parameters including, inaddition to mean left atrial and mean left atrial transmural pressures,one or more of (1) lengths of systolic time intervals, (2) contractilityindex, (3) pulse amplitude ratios while performing the Valsalvamaneuver, (4) cardiac output index, and (5) a measurement of pulse wavevelocity.

These and other objects, features, and advantages of this invention willbecome apparent to those skilled in the art after a consideration of thefollowing detailed description taken in conjunction with theaccompanying drawings wherein the same reference numerals denote thesame or similar parts or items throughout the several views and in whicha preferred embodiment of this invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a supine patient associated with the apparatus ofthe present invention.

FIG. 2 is a partial left lateral sectional view of the patient takenalong the mid-sagittal plane and showing a partially developedesophageal catheter which embodies the present invention.

FIG. 3 is a schematic view of the catheter.

FIG. 4 is a sectional view taken generally along the line 4--4 in FIG.3.

FIGS. 5 and 6 are sectional views taken generally along the lines 5--5and 6--6 respectively in FIG. 2.

FIG. 7 is a schematic view of a portion of the catheter in the esophagusand illustrating its relation to the left atrium and aortic arch in atall male adult to the right of the vertical centerline of the figure,and in a short female adult to the left of the vertical centerline, theillustration of the left atrial/aortic arch relationships along theesophagus being drawn to scale in a direction along the length of theesophagus.

FIG. 8 is a graph of a series of simultaneous wave forms at variousesophageal depths of a balloon in a relatively tall subject illustratingchanges in the balloon pressure wave form for positioning of the balloonadjacent the left atrium.

FIG. 9 is a graph illustrating a series of consecutive left atrialballoon pressure waves at various balloon inflation volumes andsimultaneous ECGs illustrating an improved method of obtaining aquantitative determination of mean left atrial pressure.

FIG. 10 is a graph of a series of simultaneous wave forms of the leftatrial and aortic balloons and ECG illustrating the obtaining ofsystolic time intervals.

FIG. 11 is a graph of a series of simultaneous wave forms of the aorticballoon and ECG illustrating an alternative method of obtaining systolictime intervals.

FIGS. 12 and 13 are each graphs of a series of simultaneous wave formsof the left atrial and aortic balloons and airway pressure illustratingrespective alternative ways of obtaining pulse amplitude ratios whileperforming the Valsalva maneuver.

FIG. 14 is a graph of an idealized left atrial balloon pressure waveform and simultaneous ECG and its relation to various heart wave formsfor use in describing the obtaining of an index of cardiac output.

FIGS. 15 and 16 are graphs or tracings, with simultaneous ECGs, of leftatrial balloon pressure in a person with leg cuffs restricting bloodflow to the legs and with the leg cuffs removed respectively andillustrating the obtaining of an index of cardiac output.

FIG. 17 is a graph or tracing of atrial balloon pressure and thesimultaneous differentiated atrial wave form.

FIG. 18 is an illustration of aortic pressure, illustrating analternative means of obtaining an index of cardiac output.

FIG. 19 is an illustration of aortic pressures taken at the aortic archand carotid artery respectively, illustrating a means of determiningpulse wave velocity.

FIGS. 20 and 21 are graphs or tracings, similar to those of FIGS. 15 and16, with simultaneous ECGs, of aortic balloon pressure in a person withleg cuffs restricting blood flow to the legs and with the leg cuffsremoved respectively and illustrating the obtaining of an alternative orsecond index of cardiac output.

FIG. 22 is a flow chart of a preferred method of determining mean leftatrial pressure.

FIG. 23 is a flow chart of a preferred method of determining systolictime intervals and components thereof.

FIG. 24 is a flow chart of a preferred method of determining pulseamplitude ratios during the Valsalva maneuver.

FIG. 25 is a flow chart of a preferred method of determining an index ofcardiac output using the left atrial balloon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT IN GENERAL

Referring to FIGS. 1 to 3, the cardiac performance apparatus fornoninvasive monitoring, indicated generally at 10, is shown associatedwith a person P, who may be a patient in a cardiac care setting. Theperson P is shown in a supine position on a hospital bed, gurney,operating table or the like, which support is indicated at 11. Theapparatus includes, as its principal components, a computer includingcontrolling and information processing means 12, and information displayapparatus including a CRT 14 and a recorder 16. The controlling andinformation processing means, which includes a computer, furtherincludes an electrocardiograph (ECG) 18 conventionally having leads 18.1and 18.2 and a ground lead (not shown), and an automaticsphygmomanometer 21 which is interconnected with a blood pressure cuff22. The cardiac performance apparatus for non-invasive monitoringadditionally includes an esophageal catheter, indicated generally at 20.The automatic sphygmomanometer and blood pressure cuff are ofconventional design and will not be described further. The ECG is alsoof conventional design. While other suitable leads, such as limb leads,could be employed with the ECG, in most cases it will only be necessaryto use "lead II" (which is the signal produced by negative lead 18.1 andpositive lead 18.2 when applied to the patient in the manner shown).Lead II will produce a good visualization of the P waves, which will beused for timing purposes as set forth below. While lead 18.1 is shownconnected to the upper right chest, it may be connected to the shoulder,or right arm. Similarly, the positive lead 18.2 is shown associated withthe lower left chest, but it may be connected to the upper left abdomen,or to the left lower leg. The trunk positions are the standard positionsused for continuous monitoring in hospitals and by paramedics andEmergency Medical Technicians.

Now, with reference to FIGS. 3 and 4, it can be seen that the catheter20 includes an integral double lumen flexible tube 24 having an outerwall 24a and an inner wall or partition 24b. These walls define lumens26.1 and 26.2, which are separated from each other by the inner wall 24bso that fluid (typically air) entering one lumen cannot enter the otherlumen. The tubing 24 is preferably an extruded biocompatible generallynon-elastic plastic such as, for example, Dow Pellethane 3883-80AEmaterial with 20% barium sulfate and 1% titanium dioxide, and has adiameter of perhaps about 0.13 inch (3.3 mm). The thickness of the outerwall 24a and of the partition 24b may perhaps be about 0.015 inch. Onthe distal end portion of the tube are mounted a pair of spaced apartballoons 28.1 and 28.2, respectively. The distal end of the double lumentube 24 terminates at a closed end, illustrated at 24d, beyond thedistal balloon 28.1, which end is suitably closed and/or sealed such asby heat seal, epoxy, or the like. Closed end 24d is located perhapsabout 1.5 cm beyond the distal balloon 28.1. The upper or proximal endportion of the tube 24 is provided with a suitable coupling 30. Thecoupling 30 connects the lumens 26.1 and 26.2 to substantially identicalfluid lines 32.1 and 32.2, respectively, for flow communicationtherebetween. Each of the lines 32.1 and 32.2 is interconnected with apressure compensated microphone (34.1 and 34.2, respectively) and apressure transducer (36.1 and 36.2, respectively), as discussedhereinafter. Each of the lines is also connected to a source of fluidunder substantially constant pressure, such as compressor 38 (FIG. 1)through suitable valves for pressurization of the respective balloon. Inorder to reduce dead space and eliminate the need for a stepping motor,the compressor 38 outlet is connected to an accumulator 40 and apressure regulating valve 42. Downstream, each line 32 may be connectedvia needle valve 44 and a solenoid operated valve 46. The flow throughthe needle valves may be suitably timed to obtain the desired balloonpressures. The balloons may alternatively be connected to separatepressure sources or to other suitable pressure sources such as describedin my aforesaid patents. The fluid conveying apparatus, which includesfluid lines 32, coupling 30, and valves 42, 44, and 46, is referred toas the "MLAP machine" in the flow charts of FIGS. 22 to 25.

The tubing 24 passes through openings in the distal and proximal ends ofeach of the balloons 28.1 and 28.2, which openings are sealed to thetube in an air tight manner so that each of the balloons can beinflated. The balloons are composed of polyurethane film or othersuitable material which is generally non-elastic yet highly compliant.When inflated, the balloons 28.1 and 28.2 have diameters, illustrated at28.1d and 28.2d, respectively, of perhaps about 8 mm and 11 mm,respectively and have suitable overall lengths as described hereinafter.Since the balloons are deflated during insertion of the catheter andsince the catheter is otherwise of small diameter, the catheter may beeasily inserted without undue discomfort to the patient. To provide forflow between the balloon and the source of fluid under pressure,inflation openings are provided in the lumen wall portions (in the tubeouter wall 24a) which are within the balloons respectively. Thus, thereare perhaps three longitudinally spaced 18 gauge (about 0.033 inchdiameter) openings 26.11 extending through the wall portion 24a of lumen26.1 which lies within the distal balloon 28.1. Similarly, there areperhaps four longitudinally spaced 18 gauge openings 26.22 extendingthrough the wall portion 24a of lumen 26.2 which lies within theproximal balloon 28.2. The number and size of such openings may vary. Inaddition to providing flow means for pressurization of the respectiveballoons, the openings are provided to facilitate, when the balloons areproperly positioned in the esophagus, as discussed below, transmissionto the pressure compensated microphones 34.1 and 34.2 of sound wavesfrom the mitral and aortic valves, respectively, for listening theretoand/or obtaining analog or digitized representations thereof.

The pressure transducers 36.1 and 36.2 process pressure waves from theballoons 28.1 and 28.2, respectively, in a manner described in myaforesaid patents. Similarly, microphones 34.1 and 34.2 process soundwaves from the balloons 28.1 and 28.2, respectively, in a manner similarto that described in my previous patents. The signals from transducers36.1 and 36.2, microphones 34.1 and 34.2, ECG leads 18.1 and 18.2, andpressures from blood pressure cuff 22 are suitably processed by thecontrolling and information processing means 12, which is programmed tosuitably process the information to obtain and display the outputsdescribed hereinafter on display apparatus 14 and 16, using principlescommonly known to those of ordinary skill in the art to which thisinvention pertains.

Referring to FIGS. 2, 5, 6, and 7, there is illustrated the placement ofthe balloons 28.1 and 28.2 within the esophagus ES of a person P for thepurpose of noninvasively obtaining and monitoring cardiac performanceparameters, as hereinafter discussed, in accordance with the presentinvention. FIG. 5 illustrates the relationship of the esophagus ES tothe left atrium LA and right atrium RA of the heart H, ascending aortaAA, lungs L, pulmonary trunk PT, descending aorta DA, and vertebrae V atthe position of placement of distal or left atrial balloon 28.1 withinthe esophagus ES, and illustrates this balloon adjacent the left atriumLA. The mitral valve MV and aortic valve AV of the heart H areillustrated in FIG. 2, which also illustrates the relationship of theleft atrium LA to the aortic arch AAR along the length of the esophagusES. FIG. 6 illustrates the relationship of the esophagus ES to theaortic arch AAR, sternum ST, superior vena cava SV, trachea TR, andvertebra V at the position of placement of proximal or aortic balloon28.2 within the esophagus ES, and illustrates this balloon 28.2 adjacentthe aortic arch AAR.

The catheter 20, which has a suitable length, which is preferably atleast about 80 cm. (from the coupling 30 to the distal end), is inserteddistal end 24d first through nasal passage NP, pharynx PH, then into theesophagus ES. If desired, the catheter may alternatively be insertedthrough the mouth. The tubing 24 desirably has markings (not shown),such as a marking at each centimeter along its length to indicate thedistance from the end 24d so that the balloons can be properlypositioned as discussed hereinafter. Although the esophagus ES isillustrated in FIGS. 2 and 7 open over its length for ease ofillustration, it is of course well known to those of ordinary skill inthe art to which this invention pertains that the esophagus is normallycollapsed and closes about any objects such as the catheter containedtherein. When the catheter is inserted to its proper depth, balloon 28.1will be positioned underneath (when the subject is in a supine position)and adjacent the left atrium LA of the heart H as shown in FIGS. 2, 5,and 7.

In accordance with the preferred embodiment of the present invention,the balloons 28.1 and 28.2 are spaced apart on the tubing 24 a distanceof, for example, about 4 cm and have lengths (suitable lengths asillustrated in FIG. 3) so that, when lower or distal balloon 28.1 isadjacent the left atrium, illustrated at LA in FIGS. 2, 5, and 7, theupper balloon 28.2 is adjacent the aortic arch, illustrated at AAR inFIGS. 2, 6, and 7, and generally below the aortic arch over asubstantial portion thereof, as best illustrated in FIG. 2. This willallow pressures adjacent both the left atrium and the aortic arch to besensed in a manner more fully set forth below. In addition, the soundsof the mitral valve MV and aortic valve AV can be picked up forprocessing without moving the catheter 20 once it is positioned.

The length of the distal balloon is desirably minimized so as to lieadjacent the left atrium over most of its length for good pressurecoupling and so as to reduce any interference by the aorta or otherwisewith its reception of the left atrial pressure waves. In accordance withthese objectives, the overall length of the balloon 28.1 is selected tobe preferably between about 1.5 and 3.5 cm, more preferably about 2.5 cm(with a taper at each end of perhaps about 0.25 cm). The overall lengthof the balloon 28.2 may suitably be about 3.6 cm (with a taper at eachend of perhaps about 0.3 cm).

FIG. 7 illustrates to the left and right sides of the centerline 48 ofan esophagus ES, the left atrial/aortic arch spatial relationships for ashort female P_(SF) (height of about 5'2") and for a tall male P_(TM)(height of about 6'1"). These illustrated relationships are drawn toscale in a direction longitudinally of the esophagus. As illustrated inFIG. 7, the distance to the left atrium centerline 50 of the femaleP_(SF) is at about 33 cm. along the catheter from the entrance to thenasal passage NP, while the distance to the left atrium centerline 52 inthe male P_(TM) is about 40 cm. from the entrance to the nasal passage.Thus, the distance to the left atrium in adults varies widely. However,as seen in FIG. 7, the distance between the left atrium LA and aorticarch AAR is substantially the same in both the tall man and the shortwoman. Furthermore, it is my belief as a medical doctor that thisdistance is substantially constant, as illustrated by FIG. 7, invirtually all adults. This substantially constant relationship allowsthe catheter to advantageously be provided in a single standardizedsize.

In order to provide a standardized catheter which will suitably fitsubstantially all adult patients so as to reduce the expense,inconvenience, and complexity inherent in carrying and using a set ofcatheters of various sizes, in accordance with the present invention,the upper balloon 28.2 is spaced away from the lower balloon 28.1 thedistance set forth above so that when the lower balloon 28.1 ispositioned adjacent the left atrium LA, the upper balloon 28.2 issuitably positioned adjacent the aortic arch AAR in either shorteradults, such as P_(SF), or in taller adults, such as P_(TM). It can beseen that with this spacing the upper balloon will not be so near thepulmonary artery PA as to receive interference from the pressurethereof. A greater distance between balloons or a greater length of theupper balloon 28.2 which would place it so high in the esophagus that agag reflex may be initiated is not considered to be desirable.

My prior aforesaid patents disclose suitable positioning of a balloonbeside the left atrium for receiving the pressure waves therefrom forsuitably obtaining determinations of mean left atrial and mean leftatrial transmural pressures. With the balloon thus suitably positioned,my prior aforesaid patents disclose suitably obtaining quantitativedeterminations, from the effects of left atrial pressure on the balloon,of mean left atrial and mean left atrial transmural pressures.

In accordance with the present invention, the balloons 28.1 and 28.2 areused along with blood pressure cuff 22 and the electrocardiogram, asneeded, to noninvasively obtain the pressures and other informationneeded for suitably monitoring cardiac performance, i.e., systolic timeintervals, an index of cardiac output, a measure of pulse wave velocity,left ventricular contractility index (dp/dt/MLAP), and pulse amplituderatios before, during, and after performing the Valsalva maneuver. Afterthe following discussion of an improvement in the obtaining of adetermination of mean left atrial and mean left atrial transmuralpressures, the use of the apparatus of the present invention forobtaining determinations of each of the above parameters of cardiacperformance will in turn be discussed. The computer may be suitablyprogrammed to implement these procedures, using principles commonlyknown to those of ordinary skill in the art to which this inventionpertains.

Positioning of Catheter

As discussed in my prior patents, the distal balloon 28.1 must becorrectly positioned adjacent the left atrium in order to suitablyobtain the wave form for determining mean left atrial and mean leftatrial transmural pressure. One suitable means of positioning the atrialballoon utilizes a bi-polar electrode (which comprises two spacedelectrodes, illustrated at 51 in FIG. 7), which is attached to thecatheter 20 just above the balloon 28.1, as disclosed in my U.S. Pat.No. 5,570,671. The bi-polar electrode leads, illustrated at 51a and 51bin FIG. 4, are preferably embedded in the material which forms thedouble lumen catheter in order to prevent their interference withpressure signals. As the electrode 51 is moved up the esophagus, itssignals are used to obtain an electrogram at each of a series ofincremental depths. The length of the negative portion of the largestabsolute value of the P wave is determined for at least one P wave ineach incremental electrogram. The depth to the center of the left atriumis selected to be that which corresponds to the incremental electrodedepth at which the electrogram therefor shows the greatest negativeportion length. The balloon 28.1 is then positioned at that selecteddepth for obtaining the cardiac performance information as hereinafterdiscussed.

While the above means for positioning the balloon 28.1 is considered tobe very reliable, the bi-polar electrode adds additional cost to thecatheter, and there is "wait" time at each increment of position untilthe electrogram readings "settle down." In order to eliminate the needfor esophageal electrodes, as well as to provide an alternative meansfor balloon positioning, in accordance with the present invention, theballoon 28.1 may be alternately positioned, if desired, in accordancewith the following procedure. With the balloon 28.1 in the stomach (notshown), it is inflated to a suitable pressure of perhaps 6 cm. waterpressure. While thus pressurized, the catheter 20, which may be suitablymarked at perhaps 1 cm. increments, is drawn up the esophagus startingat a suitable depth of perhaps about 48 cm (from tip of nose to centerof balloon 28.1) which is known to be well below the position of theleft atrium. Each of the depths is manually inputted to the controllingand information processing means 12.

With reference now to FIG. 8, a five channel graph is illustrated, withsegments of the graph being produced at various balloon depths. Thus,the five channel tracing to the left of FIG. 8 shows tracing of balloonpressure at a catheter depth of 44.5 cm. FIG. 8 also shows tracings atdepths of 37.5 cm, 36.5 cm, 35.5 cm, 34.0 cm and 33.0 cm. These tracingsare for the tall male P_(TM). With reference to FIG. 7, it can be seenthat at a depth of 44.5 cm, the top of the balloon 28.1 is barelyadjacent the bottom of the left atrium LA. However, it can be seen frompressure tracing 202, and more particularly the high gain tracing 204,that the balloon has been pulled up to such an extent that the pressurewithin the balloon is being influenced by the filling and emptying ofthe left atrium. This is also shown by the oscillometric waveform 208.All of these tracings are based on signals sent to the controlling andprocessing means 12 by the transducer 36.1, the means 12 causing thesewaveforms to be transmitted to the monitor 14 and the recorder 16. Themeans 12 also receives inputs from the ECG leads 18.1 and 18.2 (leadII), and from the microphone 34.1, (as well as from other inputs), andtracings representative of these signals are shown at 206 and 210,respectively.

While tracings produced by recorder 16 may be used, it is envisionedthat most health care professionals will use the monitor 14 to positionthe catheter. The monitor 14 may, for example, display the balloonpressure 204, depth of distal balloon, oscillometric wave form 208, andsimultaneous ECG wave 206 for perhaps the three most recent distalballoon depths so that the balloon pressure waves 204 at these depthsmay be compared.

As seen in FIG. 8, the tracing 204 of high gain raw balloon pressureshows a modified a, c, v wave form at balloon depths of 44.5 and 37.5cm. (The balloon pressure wave form is referred to as a modified a, c, vwave form because the "a" peak of the balloon wave form is inverted fromthe "a" peak of the a, c, v wave form, illustrated at 392 in FIG. 14, ofpressures taken from within the left atrium. This wave form is notunusual in some patients. Both troughs and peaks in the wave form, whichare points where the slope of the wave form changes between positive andnegative and which are indicated in FIGS. 8, 9, and 14 by "a", "c", and"v", are referred to herein as "peaks". The wave portions which containthese "a", "c", and "v" peaks are referred to as "a", "c", and "v"waves, respectively. FIG. 9 illustrates an externally derived pressuremeasurement technique which may not work in all persons. The a, c, vwave form extends generally between points 371 and 373 on the idealizedatrial balloon pressure curve 370 of FIG. 14.

I have now determined that there is a depth in the esophagus at whichthere is a major change in the balloon pressure wave form 204 so thatthe left atrial pressure (a, c, v) wave form is no longer apparent.Moreover, the amplitude of the wave form at this depth has abruptlysubstantially increased, further indicating that the balloon pressure isbeing affected by a different pressure source within the body. It isbelieved that the new wave form, illustrated at 212, at the higherdepths (36.5 cm and 35.5 cm in FIG. 8) may be a wave form caused by thepulmonary artery PA. More importantly, the characteristic left atrialpressure wave form with its much smaller amplitude is no longer apparentat the 36.5 cm depth, indicating that the balloon 28.1 has moved beyondthe position of the left atrium. In accordance with the presentinvention, the balloon 28.1 is thus positioned at a catheter depthslightly below the uppermost depth (36.5 cm in FIG. 8) at which thecharacteristic left atrial pressure wave (a, c, v) first disappeared.Taking into consideration the size of the left atrium, it is consideredpreferred that the balloon 28.1 be lowered from this depth (36.5 cm)perhaps about 2 to 3 cm (to a depth of perhaps about 39 cm in thissubject) until a good left atrial pressure wave form is seen, and themonitor 14 may be used as an aid in such positioning. The catheter 20may then be secured to the nose or lip, and the various measures ofcardiac performance described hereinafter obtained with the distalballoon 28.1 in position adjacent the left atrium and the proximalballoon 28.2 confidently in position adjacent the aortic arch.

The left atrial pressure signal may be subjected to fast Fouriertransform analysis, in accordance with principles commonly known tothose of ordinary skill in the art to which this invention pertains, tocorrect each frequency component for amplitude and phase shift using asuitable regression equation for the catheter, including a factor forbarometric pressure. The true left atrial pressure signal isreconstructed by adding all corrected frequencies, and the correcttiming of the wave form reestablished with the ECG.

While positioning of the balloon 28.1 has been 30 described, it shouldbe appreciated that the balloon 28.2, which is maintained in the samespatial relationship to the balloon 28.1, will accordingly be positionedas shown in FIG. 7. Also, while the distances used are for the tall maleP_(TM), the same positioning technique would be used for other persons.Thus, as can be seen from FIG. 7, the balloon 28.1 would be moved downfor person P_(SF) 2-3 cm after the waveform 212 had been detected.

The aortic balloon 28.2 may alternatively be positioned, after placingit deep in the esophagus and suitably inflating it to, for example, 6 cmof water, bringing the balloon 28.2 slowly up the esophagus such as in 1cm increments and looking for the typical aortic pressure signal, whichwill be inverted, for reasons discussed hereinafter, using the ECG fortiming. Other suitable means may of course be used for positioning theleft atrial and/or aortic balloons.

Determining Mean Left Atrial Pressure and Mean Left Atrial TransmuralPressure

My prior aforesaid patents disclose methods using the oscillometricprinciple for determining quantitatively mean left atrial and mean leftatrial transmural pressures. In accordance with these methods, pressurein a balloon adjacent the left atrium is gradually raised, and theballoon pressure, at peak amplitude of the balloon pressure oscillations(or the peak amplitude of sound waves passing through the inflatedballoon) effected by the pressure outside the balloon is noted. Inaccordance with the oscillometric principle, this balloon pressure isequal to the mean pressure outside the balloon which is acting on it. Inother words, when the wall of the left atrium is unloaded such that themean transmural pressure gradient is zero, the transmission of pressurechanges is optimal and is not influenced by compliance of the atrialwall.

It is however believed that the balloon 28.1 may (in some patients) pickup aortic pressure waves (from the descending aorta) which may combinewith the left atrial pressure waves and thus skew the results. It isalso believed that this effect is predominant during the period of timebetween the "c" and "v" atrial wave peaks when rapid changes in aorticpressure are occurring and that this effect is insubstantial during theperiod of time of the "a" wave portion (which includes wave portions 371and 372 of the atrial wave form, or between the P wave and the peak ofthe QRS complex on the ECG, when aortic pressure 390 tends to berelatively constant (as is illustrated in FIG. 14). Therefore, withreference now to the pressure wave of balloon 28.1, as shown at 220 inFIG. 9, in order to more precisely obtain a determination of mean leftatrial and mean left atrial transmural pressures, at least in somepatients, in accordance with the present invention, the balloon pressureduring the "a" wave portion is used (instead of the entire wave form)for determination thereof, as discussed hereinafter.

With the catheter 20 in position, the proximal (aortic) balloon 28.2 isevacuated to perhaps about -20 mm Hg after which perhaps about 0.5 ml ofair is added. This balloon 28.2 is connected to the transducer 36.2 tomeasure esophageal pressure continuously. The distal (atrial) balloon28.1 is evacuated to perhaps about -20 mm Hg then filled at a rate ofperhaps about 0.01 ml free air per second.

FIG. 9 shows representative segments A1 to A5 of a series of five graphsor balloon pressure tracings of the actual left atrial pressure waveform220, amplified by a 10-fold increase in gain and having a simultaneousECG 300 for timing, in the tall male in a supine position with theballoon pressure steadily increased by adding air in increments of 0.05ml to the balloon. Thus, the wave form 220 in segments A1 to A5 are withthe balloon pressure increased to have balloon volumes of 0.75 ml, 0.80ml, 0.85 ml, 0.90 ml, and 0.95 ml of air respectively.

Using the ECG 300 for timing, the "a" wave portion, which is part of theentire left atrial pressure wave 220, is identified and the peak to peakvoltage, illustrated at 237, of the "a" wave portion 371 or 372 havingthe highest voltage (highest amplitude) is measured at each of theballoon volumes A1 to A5 and stored in computer memory. This peak topeak voltage 237 is a measure of the "a" wave amplitude and representsthe maximum voltage difference recorded from the atrial wave form duringthe time period from the P wave to the peak of the QRS complex on theECG.

The signals are subjected to fast Fourier transform analysis, inaccordance with principles commonly known to those of ordinary skill inthe art to which this invention pertains, to correct each frequencycomponent for amplitude and phase shift using a suitable regressionequation for the catheter. The true left atrial pressure signal is thenreconstructed by adding all corrected frequencies and the correct timingof the wave form re-established with the ECG.

When the left atrial balloon filling cycle is completed, therecordations of the balloon pressure at preferably end-expiration areexamined, such as by use of a suitably programmed computer, and the timewhen one or more, such as 5, contiguous "a" wave portions at a certainballoon volume reached the highest recorded voltages, corresponding topeak oscillation pressure, is identified. The balloon pressures fordetermining mean left atrial and mean left atrial transmural pressuresshould be taken at the same point in the respiratory cycle, which ispreferably end-expiration. The pressure in atrial balloon 28.1 at thattime is identified and displayed on the screen.

Alternatively or additionally, the heart sounds passing through theinflated balloon 28.1 are recorded by pressure compensated microphone34.1 and suitably digitized, as discussed more fully in my aforesaidU.S. Pat. No. 5,570,671. The mean balloon pressure at preferablyend-expiration at the sound wave peak amplitude is suitably inputted tothe computer and displayed on the monitor, and the mean left atrial andmean left atrial transmural pressures are determined therefrom anddisplayed as discussed herein for balloon pressure oscillations.

As discussed in my prior patents, there is an abrupt slope change from afast to a slowed rate of pressure increase indicative of theequalization of balloon pressure with the surrounding tissue pressureprior to balloon expansion. This slope change pressure is determinedfrom the atrial balloon pressure-volume curve and inputted to thecomputer. In order to determine mean left atrial transmural pressure,the pressure (preferably end-expiratory pressure) at this slope changeis subtracted from preferably end-expiratory pressure at the balloonoscillation peak, and this pressure may then be displayed by themonitor.

Referring to FIG. 17, there is illustrated at 240 a graph or tracing ofpressure in the atrial balloon while adjacent the left atrium and at 242a simultaneous graph or tracing of balloon pressure oscillations.Tracings 240 and 242 are similar to those of FIGS. 9 and 11 respectivelyof my aforesaid U.S. Pat. No. 5,263,485, except as hereinafterdiscussed. The abrupt slope change indicative of the equalization ofballoon pressure with the surrounding tissue pressure prior to balloonexpansion is shown at 244. The signal for tracing 242 has beendifferentiated by use of a conventional analog or digitaldifferentiator. As the signal peaks, the rate of voltage changeincreases, which is displayed by the differentiator. Advantageously, itis not necessary to filter out low frequencies with this technique. Asseen in FIG. 17, the differentiated signal allows one to more clearlysee the point of oscillation peak 246 so that mean left atrial and meanleft atrial transmural pressures may be more precisely determined.

From the proximal (aortic) balloon 28.2, the esophageal end-expiratorypressure is obtained and inputted to the computer. In order to determinemean left atrial pressure, the esophageal end-expiratory pressure isadded to the mean left atrial transmural pressure, and this pressure mayalso be displayed by the computer.

It was seen in the wave form segments A1 to A5 of FIG. 9 that the peakamplitude 237 of the "a" wave portion 222 occurred at a balloon volumeof 0.85 ml (segment A3), which corresponds to a peak oscillationpressure of 16 cm water, which corresponds to a mean left atrialpressure of about 9.5 to 10 mm Hg, which is considered to be a normalvalue.

The measurement cycle may be repeated at a preset sampling frequency,and the information printed out and used as needed and for thedetermination of other cardiac performance parameters as discussedhereinafter.

A preferred method for determining mean left atrial pressure inaccordance with the above discussion is illustrated generally at 650 inthe flow chart of FIG. 22.

Determining Systolic Time Interval and Components Thereof

The systolic time interval (QS₂) comprises the duration of time from thebeginning of the Q wave on the electrocardiogram to the time of thesecond heart sound S₂, which is in this case the sound of the aorticvalve closing. During this time interval there are the two components orphases of left ventricular systolic activity, i.e., the pre-ejectionperiod (PEP) and the left ventricular ejection time (LVET). PEP refersto the time spent by the ventricle increasing pressure on the volume ofblood in it before ejection of the blood into the aorta, and LVET is theduration of the ejection phase. These time interval components may beused in various combinations to gauge ventricular performance. Forexample, a long PEP indicates that the heart is pumping againstincreased resistance, and the ratio PEP/LVET is known to decrease ascardiac output increases.

In order to reliably, conveniently, inexpensively, and continuouslyobtain systolic time intervals and components thereof, in accordancewith the present invention, the catheter 20 and the ECG 18 are usedpreferably in combination, the catheter being provided with a pressurecompensated microphone 34.2 with a 100 Hz high pass filter to create anaortic phonocardiograph. Thus, after the catheter is suitablypositioned, as hereinbefore discussed, and the aortic balloon 28.2 issuitably inflated to a minimal pressure of perhaps about 2 to 4 mm Hg,the aortic pressure wave form from balloon 28.2, illustrated at 314 inFIG. 10, is suitably recorded and digitized, using the ECG for timing.The phonocardiogram, illustrated at 308, is also suitably recorded. Theaortic wave form is desirably analyzed with fast Fourier transformanalysis to correct phase shift and frequency components found usingsuitable equations for the catheter dimensions, and the aortic wave formis then reconstructed by adding the corrected frequency components.

The exemplary aortic pressure signal 314 shown in FIG. 10 was taken withthe subject sitting up. When a subject is lying flat, this signal may beinverted due perhaps to the aortic arch moving apart during systole. Ifthe signal is inverted, it should desirably be re-verted electronicallyto show pressure increases during ventricular ejection.

Referring to FIG. 10, the time of onset Q (302) is obtained from theECG, illustrated at 300, the QRS complex being shown at 303. The ECG istaken from lead II of the skin ECG. The time of S₂ is taken as the timeof beginning, illustrated at 304, of the second heart sound, illustratedat 306, from the aortic phonocardiogram 308. The length of time of thetotal systolic time interval QS₂ is the time interval between times 304and 302.

The beginning of LVET is taken as the time of beginning, illustrated at310, of the upslope, illustrated at 312, of the aortic pressure signal,illustrated at 314, which indicates that the left ventricle has begundischarging blood into the aorta. The aortic pressure signal wave form314 is taken from the balloon 28.2 adjacent the aortic arch.

The end of LVET is taken as the time, illustrated at 316, of thedicrotic notch, illustrated at 318, of the aortic wave form 314. Thedifference between times 316 and 310 is the LVET. If the dicrotic notchis badly distorted because of aortic valve pathology, LVET determinationmay have to be aborted.

PEP is the difference between QS₂ and LVET. However, PEP is stillobtainable even if LVET cannot be obtained, as being the differencebetween times 310 and 302. Thus, while the use of the aorticphonocardiogram is preferred, this is an alternative way of obtaining adetermination of PEP whereby at least one and perhaps both phases of thesystolic time interval may be determined without the use of aphonocardiogram at all.

If desired for the purpose of determining PEP, the time 310 of beginningof upslope 312 of aortic pressure wave 314 may be suitably corrected forthe time delay due to the distance from the aortic valve to the aorticballoon (the correction should be approximated by a constant and shorttime delay), using principles commonly known to those of ordinary skillin the art to which this invention pertains. However, I believe that theuncorrected time 310 may be normally sufficiently precise fordetermination of PEP as well as LVET.

FIG. 10 also shows at 319 and 320, respectively, the simultaneous leftatrial pressure signal and the unfiltered left atrial phonocardiogramfrom the distal (atrial) balloon 28.1.

The PEP is suitably corrected for heart rate (PEP+0.4HR), the LVET issuitably corrected for heart rate and sex (LVET+1.7 HR for men, LVET+1.6HR for women), and the QS₂ is suitably corrected for heart rate and sex(QS₂ +2.1 HR for men, QS₂ +2.0 HR for women). For beat by beat analysis,these determinations may be meaned for perhaps 10 beats and may besuitably displayed.

Referring to FIG. 11, there is illustrated an alternative procedure fordetermining LVET. Using the simultaneous ECG 300 for timing, a rawaortic pressure signal (with the proximal balloon 28.2 inflated to avolume of perhaps about 0.7 ml air) is illustrated at 330, and thissignal is suitably differentiated to obtain differentiated aortic signal332. The sharp upslope beginning at point 334, which occurs at the endof the QRS wave, is believed to signal the beginning of LVET. The point336 is believed to signal the end of LVET because of aortic valveclosure (illustrated at AC in FIG. 14) at this point. Thus, LVET, inaccordance with this alternative embodiment of the invention, isbelieved to be the duration of time between points 334 and 336.

A preferred method for determining systolic time intervals andcomponents thereof in accordance with the above discussion isillustrated generally at 660 in the flow chart of FIG. 23.

The ratio PEP/LVET is considered to be a useful index of ventricularperformance, with a minimum value indicating optimum performance.

Determination of Pulse Amplitude Ratios During Valsalva Manner

The Valsalva maneuver involves having a patient create and maintain anairway pressure with open glottis by blowing into a mouthpiece topressurize a mercury column to 40 mm Hg. (or, if the patient cannotgenerate this pressure, perhaps 20 to 25 mm Hg.) and holding it therefor 10 seconds. By examining the arterial blood pressure during andimmediately after this maneuver, a diagnosis of heart failure may bemade since a normal heart and a heart in hypertensive heart failurerespond to the maneuver in different ways, as discussed in "Effects ofValsalva's Maneuver on the Normal and Failing Circulation" by E. P.Sharpey-Schafer, British Medical J., Mar. 19, 1955, p. 693 to 695. Ahealthy heart shows an increase in pulse pressure then damping of thepressure during the Valsalva maneuver, followed by a dramatic increasein pulse pressure and decrease in heart rate with rapid damping of thepulse pressure when the Valsalva maneuver is released. A diseased heartdoes not respond in this fashion.

In accordance with the present invention, the catheter 20 is used toconveniently and reliably provide a wave form of (1) left atrialpressure by use of the distal (atrial) balloon 28.1 similarly aspreviously discussed and/or (2) aortic pressure by means of proximal(aortic) balloon 28.2 (while inflated to perhaps about 6 mm Hg) aspreviously discussed. Each of these wave forms will show thecharacteristics of a normal or failed heart, as the case may be, duringand immediately after the Valsalva maneuver is performed.

Instead of being connected to a mercury column, the mouthpiece mayinstead be connected to a precalibrated transducer and feedback ofairway pressure provided to guide the patient. Alternatively, esophagealpressure can be used to demonstrate the Valsalva maneuver withoutrecourse to airway pressure by using the atrial or aortic balloons. Thepatient should be sitting in an upright position in order for esophagealpressure measurements to be provided by the atrial or aortic balloon,which is evacuated to perhaps about -20 mm Hg., then filled with perhapsabout 0.4 ml air for this purpose.

FIG. 12 illustrates one method of measuring pulse amplitude ratiosfollowing the Valsalva maneuver. Illustrated at 350 is an increase inesophageal pressure (about 30 cm water) as determined by the aorticballoon for a period of time (about 10 seconds) as the Valsalva maneuveris being performed by an upright subject. This is confirmed bysimultaneous increased airway pressure (about 40 cm water), illustratedat 352, for the same period of time. Immediately after performance ofthe Valsalva maneuver, the left atrial balloon wave form, illustrated at354, shows a dramatic increase in left atrial pressure, and a decreasein heart rate, characteristic of a normal heart. In order that the pulseamplitude pattern of the left atrial balloon pressure may be easy toview and work with, in accordance with the present invention, the leftatrial pressure oscillometric wave form 354 is preferably placed on asteady baseline, in accordance with procedures discussed in my aforesaidpatents and using principles commonly known to those of ordinary skillin the art to which this invention pertains.

FIG. 13 illustrates an alternative method of measuring pulse amplituderatios following the Valsalva maneuver. Illustrated at 360 is anincrease in esophageal pressure (about 30 cm water) as determined by theleft atrial balloon for a period of time (about 10 seconds) as theValsalva maneuver is being performed by an upright subject. This isconfirmed by simultaneous increased airway pressure (about 40 cm water),illustrated at 362, for the same period of time. (Airway pressure ismeasured by a transducer associated with the mouthpiece.) Immediatelyafter performance of the Valsalva maneuver, the pressure, illustrated at364, in the proximal or aortic balloon 28.2 shows a pulse amplitudepattern of aortic pressure characteristic of a normal heart. In orderthat the pulse amplitude pattern of the aortic balloon pressure may beeasy to view and work with, the aortic balloon pressure wave form 364 isalso preferably placed on a steady baseline.

A preferred method for determining pulse amplitude ratios during theValsalva maneuver in accordance with the above discussion is illustratedgenerally at 670 in the flow chart of FIG. 24.

Determination of Index of Cardiac Output

In FIG. 14, the pressure in the left atrial balloon 28.1, which has beenfilled with a gas in accordance with the oscillometric principle setforth above, is illustrated ideally by line 370. FIG. 14 also ideallyillustrates, for purposes of relating the timing of various heart eventswith the atrial balloon pressure line 370, aortic, left atrial, and leftventricle pressures, illustrated at 390, 392, and 394 respectively, andthe times of closing MC of mitral valve MV, opening AO of aortic valveAV, closing AC of aortic valve AV, and opening MO of mitral valve MV.The first and second heart sounds are indicated as occurring at times S₁and S₂ respectively.

In accordance with the present invention, an index of cardiac output isobtained which is based on my belief that the "a" wave portion (causedby left atrial contraction), the "c" wave portion thereof (caused byleft ventricular contraction), and the "v" wave portion thereof (causedby pulmonary venous return to the left atrium) of the balloon-sensedleft atrial wave form 370 will each increase or decrease in proportionto an increase or decrease in cardiac output, each wave reflecting adifferent manifestation of cardiac activity. In order to accomplishthis, the area under the left atrial balloon pressure curve 370 during aheart beat may be integrated to obtain an index of cardiac output. Inorder to do so efficiently, the ECG electrodes 18.1 and 18.2 areconnected to the surfaces of the skin of the person P and the catheter20 is properly positioned with the left atrial balloon 28.1 behind theleft atrium (or below if the person P is supine). The left atrialballoon 28.1 is then suitably pressurized, as previously discussed, topeak oscillation pressure (to unload the left atrial wall, thetransmural pressure being at this time zero) and is then held at thatpressure. As previously discussed, in accordance with the oscillometricprinciple, when the balloon pressure is at peak oscillation pressure,this balloon pressure is equal to the mean pressure outside the balloonwhich is acting on it so that the wall of the left atrium is unloaded(the mean transmural pressure gradient is zero). The transmission ofleft atrial pressure changes is, during this unloaded state, optimal andis not influenced by compliance of the atrial wall. Both the ECG and aphonocardiogram from the left atrial balloon are displayed on the CRTmonitor 14 in real time. The health care personnel will evaluate thewave forms being displayed and make a judgement as to whether or not themitral valve is damaged, which may invalidate the measurements due toback flow of blood from the left atrium.

A preferred method for determining an index of cardiac output using theleft atrial balloon pressure wave form in accordance with the abovediscussion is illustrated generally at 680 in the flow chart of FIG. 25.

Referring to FIGS. 15 and 16, there are shown at 400 and 402respectively representative tracings of high gain balloon pressure withthe balloon in the esophagus adjacent and under the left atrium of aperson, and simultaneous ECGs 300. For each of these tracings 400 and402, an area, illustrated at 401 and 403 respectively (which areas arehatched for ease of illustration) was defined under the respective curvefor the length of a single heartbeat, i.e., from the beginning of oneQRS complex to the beginning of the next QRS complex, to a base line,illustrated at 405, which corresponds to the lowest pressure during thecycle. Balloon pressure 400 was taken with leg cuffs restricting bloodflow from the legs so that a low cardiac output would be expected.Balloon pressure 402 was taken with the leg cuffs off so that greatercardiac output would be expected. As seen in FIGS. 15 and 16, the area403 for balloon pressure 402 is greater than area 401 for balloonpressure 400 indicative of greater cardiac output for tracing 402, whichis consistent with the leg cuffs being off. By use of impedancecardiography, an increase of 24 per cent in cardiac output was measuredin the same person (at a different time but under similar conditions)when the leg cuffs were removed, thus confirming the usefulness of thearea under an atrial pressure wave form for determining an index ofcardiac output.

Referring to FIG. 18, there is illustrated an alternative means ofobtaining an index of cardiac output (referred to herein as a secondcardiac output index) utilizing the aortic pressure 314 as sensed by theaortic balloon 28.2 adjacent the aortic arch. This is based on theprinciple that pressure follows volume in the aorta (and elsewhere inthe vascular system), i.e., as the stroke volume (the volume of bloodflowing in the aorta during each heart beat) increases, the pressureincreases, and as stroke volume decreases, the pressure decreases. FIG.18 shows the aortic balloon pressure curve inverted, i.e., when theballoon pressure is shown to be increasing, it is actually decreasing.Thus, for analysis purposes, the aortic balloon pressure curve 314 isinverted to properly reflect the pressure within the balloon and tissuesadjacent the aortic arch. This is because, in theory, the aortic archAAR, responding to increased flow in the aorta and therefore increasedpressure, will open or tend to straighten (the ascending and descendingaorta AA and DA respectively move away from each other) like a Bourdontube as the pressure rises during systole, and the opening or tendencyto straighten of the aortic arch (resulting, with reference to FIG. 6,in the descending aorta DA tending to move away from the aortic balloon28.2 while the ascending aorta AA remains firmly fixed to the heart)will relieve force acting on the aortic balloon in the esophagus to thusdecrease aortic balloon pressure. Similarly, pressure in the aorticballoon will increase when the aortic arch closes as the aortic pressuredrops. The observation that the pressure recorded by an esophagealballoon adjacent the aortic arch was inverted with respect to the actualintraaortic pressure was made by Taquini in 1940. See Taquini, "TheEsophageal Pulse Under Normal and Abnormal conditions", The AmericanHeart Journal, vol. 40 (no.2), 129-140 (1940).

During systole, the stroke volume is the sum of arterial uptake andsystolic runoff or drainage. The arterial uptake is the volume of bloodstored in the aorta as a result of distension, this volume beingreturned to the circulation as diastolic runoff. The arterial uptakeacts to increase the aortic blood pressure as previously stated.

Systolic runoff is believed to deflect the aortic arch as a result ofNewton's third law of motion acting within the curve of the aortic arch.Thus, blood that is being propelled out and around the aortic arch bythe pumping action of the heart exerts a force on the aorta which tendsto deflect it. Thus, it is believed that both flow through (systolicrunoff) and the arterial uptake may tend to deflect the aortic arch. Byinverting the aortic balloon pressure wave form, the wave form 312 isobtainable which is thus considered to be proportional to aorticdeflection. This being so, the area under the inverted pressure/timecurve 314 of the aortic balloon pressure wave (for one heart beat) maybe determined by suitably filtering the signal digitally andintegrating, and this area is believed to be proportional to blood flowor stroke volume, i.e., it indicates greater or lesser flow through theaorta as the inverted balloon pressure curve increases or decreasesrespectively. Thus, this area is believed to provide an index of cardiacoutput when multiplied by heart rate.

The full line pressure wave 314 is for a higher pressure/flow. Thedotted line pressure wave 502 is illustrated for a lower pressure/flow.In accordance with the present invention, the area under the wave, whichthus indicates greater or lesser volume flowing through the aorta, isaccordingly integrated and multiplied by the heart rate to determine anindex of cardiac output.

Referring to FIGS. 20 and 21, there are shown at 400 and 402respectively representative tracings, inverted, of aortic balloonpressure with the balloon in the esophagus adjacent the aortic arch AARof a person, and simultaneous ECGs 300. Tracings thereof, suitablyfiltered to remove respiratory excursions, are illustrated at 604 and606 respectively, and the dicrotic notch is illustrated at 608.Illustrated at 610 and 612 are simultaneous tracings of heart soundrecordings respectively, illustrating the first and second heart soundsat 614 and 616 respectively. Illustrated at 626 and 628 are tracings ofabsolute aortic balloon pressures therefor respectively. The period ofthe heart beat for tracing 604 is shorter than that of tracing 606because of irregular heart beat due to atrial flutter. For each of thesetracings 604 and 606, an area, illustrated at 618 and 620 respectively(which areas are hatched for ease of illustration) was defined under therespective curve for the length of a single heartbeat, i.e., from thebeginning, illustrated at 622, of one QRS complex to the beginning 622of the next QRS complex, to a base line, illustrated at 624, whichcorresponds to the lowest pressure during the cycle. Balloon pressure604 was taken with leg cuffs restricting blood flow from the legs sothat a low cardiac output would be expected. Balloon pressure 606 wastaken with the leg cuffs off so that greater cardiac output would beexpected. As seen in FIGS. 20 and 21, the area 618 for balloon pressure604 per unit elapsed time is less than area 620 for balloon pressure 606(despite differences in heart rate) indicative of greater cardiac outputfor tracing 606, which is consistent with the leg cuffs being off. Byuse of impedance cardiography, an increase of about 25 per cent incardiac output was measured in the same person (at a different time butunder similar conditions) when the leg cuffs were removed, thusconfirming the usefulness of the area under an inverted aortic pressurewave form for determining an index of cardiac output.

A preferred process for obtaining the second cardiac output index (usingthe aortic pressure wave form) includes the following steps:

a. Connect the skin ECG for timing;

b. Check for any air leaks in the catheter or MLAP machine;

c. Insert catheter into the stomach via esophagus;

d. Position catheter with the distal (left atrial) balloon behind theleft atrium per "MLAP Process." This automatically positions the aortic(proximal) balloon;

e. Deflate the left atrial balloon;

f. Select the frequency of desired measurement;

g. Evacuate aortic (proximal) balloon to -20 mm Hg;

h. Gradually fill the aortic balloon with air until a slope change ofthe pressure-time curve is encountered, then stop filling;

i. Add 1.0 ml air to the balloon and close valve. No air is to be addedor removed thereafter until measurement is completed;

j. Monitor the pressure from the aortic balloon using the differentialtransducer and the low-pass filter to remove fluctuating pressureeffects from respirations;

k. Invert the pressure waveform to make it appear upright and display onthe monitor;

l. Record the aortic balloon pressure waveforms for several heart beats(for example, 6) at end expiration;

m. Using the ECG for timing, correct the pressure waveform for eachheart beat using fast Fourier analysis;

n. Calculate the waveform pressure-time integral for each heart beatrelative to a baseline that is defined by the lowest pressure seenduring each heart beat;

o. Calculate the mean pressure-time integral by summing all 6pressure-time integrals and dividing by 6;

p. Calculate the average heart rate that occurred while measuring the 6aortic pressure signals using the ECG;

q. Multiply the mean pressure-time integral by the average heart rate.This number is an index of cardiac output;

r. Display the index of cardiac output on the monitor and store ittogether with the date and time for future reference;

s. The computer compares the current index of cardiac output with priorindices and displays the results on the monitor as "percent changes incardiac output";

t. At a preselected time interval, return to step F.

Preferably, while the wave forms (left atrial or aortic) are beingevaluated on the monitor, or perhaps on chart paper from the recorder16, the information processing means will collect, for example, six (6)pressure cycles (preferably at end expiration) and corresponding ECGsand will digitize them. The processor 12 is suitably programmed toestablish for each wave form a base line corresponding to the lowestpressure observed during the respective heartbeat. The pressure-timeintegrals are then calculated, summed, and then divided by the number ofwave forms to yield a mean value. This mean value is then multiplied bythe average heart rate that occurred during the measurements (fromanalyzing the ECG). This yields an individual index of cardiac outputwhich may then be compared with subsequent or prior indexes to determinewhether cardiac output is increasing, decreasing, or remaining constant.

If it is determined that the mitral valve is damaged, the resultingback-flow may invalidate the use of the left atrial pressure wave forobtaining an index of cardiac output, it is preferred in thiscircumstance to obtain an index of cardiac output using the aorticballoon and aortic pressure wave form (which would not be affected bysuch back-flow).

The above procedures for obtaining an index of cardiac output may workwell for people with various heart conditions such as atrial flutter.

While preferably an area under an aortic or left atrial wave form may besuitably processed and integrated and multiplied by heart rate to obtainan index of cardiac output, FIGS. 15 and 16 illustrate that such aprecise analysis may not be necessary in all situations since thedifferences in area may often be merely eye-balled to give health carepersonnel the information needed to determine whether a patient'scardiac output is increasing or decreasing or staying the same.

Alternatively, slopes of certain segments of the left atrial and aorticpressure wave forms may be measured to provide an index of cardiacoutput. However, it is believed that the area under an aortic or leftatrial pressure wave, being more comprehensive, provides a more reliableindex of cardiac output.

Measuring Pulse Wave Velocity

Pulse wave velocity can be used as an index of arterial rigidity. Inorder to determine pulse wave velocity, in accordance with the presentinvention, the distance between the aortic arch and an other artery isdivided by the time difference between the pulse at the aortic arch andthe pulse at the other artery for the same heartbeat. Thus, the pressurewave form from the aorta is compared with the pressure wave form fromanother artery. Accordingly, an esophageal balloon is positioned next tothe aortic arch, and a point on the pressure wave from the balloon,after being suitably corrected by fast Fourier transform analysis, iscompared with the corresponding point on the pressure wave from thecarotid (or other suitable) artery which may be picked up by aplethysmograph or by a low frequency microphone or otherwise suitablypicked up. The aortic wave may be used to determine the pulse wavevelocity by determining the onset of the pulse wave (indicative ofopening of the aortic valve) at, for example, the aortic arch and atanother suitable artery, for example, the carotid artery, determiningthe difference in time and distance there between and deriving therefromthe velocity by dividing the distance by the time in accordance withconventional principles. As the artery becomes more rigid, the pulsewave velocity generally increases. Thus, the pulse wave velocity may beused as an index of artery rigidity, and stroke volume capacity may alsobe inferred therefrom. Referring to FIG. 19, in order to provide meansfor easily and reliably determining pulse wave velocity which can beused by paramedical personnel with minimal training, in accordance withthe present invention, the aortic pressure wave form 314 provided by theaortic balloon 28.2 adjacent the aortic arch is suitably corrected byfast Fourier analysis, in accordance with principles commonly known tothose of ordinary skill in the art to which this invention pertains.Preferably, the time period between onsets 310 and 510 of the aorticballoon and carotid (or other) artery signals respectively aredetermined since the wave tends to become distorted (becomes narrowerand higher) with increased distance from the aortic arch. Thus, the timeperiod, illustrated at 500, between the corrected time 310 of onset ofthe aortic balloon signal 314 and the time 510 of onset of the carotidartery signal 514 of the pulse wave as taken by a plethysmograph 504 issuitably calculated, using principles commonly known to those ofordinary skill in the art to which this invention pertains, and thepulse wave velocity, an index of artery rigidity, derived therefrom aspreviously discussed.

A preferred process for measuring pulse wave velocity includes thefollowing steps:

a. Connect a skin ECG for timing;

b. Check for air leak in the catheter or MLAP machine;

c. Insert the catheter into stomach via the esophagus;

d. Position the catheter with the distal (left atrial) balloon behindthe left atrium per the "MLAP Process", which will automaticallyposition the proximal (aortic) balloon;

e. Deflate the left atrial balloon;

f. Select the frequency of the desired measurement;

g. Evacuate the aortic (proximal) balloon to -20 mm Hg;

h. Gradually fill the aortic balloon with air until a slope change ofthe pressure-time curve is encountered, then stop filling;

i. Add 1.0 ml air to the balloon and close valve. No air is to be addedor removed thereafter until the measurement is completed;

j. Monitor the pressure from the aortic balloon using a differentialtransducer and low-pass filter to remove fluctuating pressure effectsfrom respirations;

k. Invert the aortic balloon signal to make it appear upright;

l. Attach a plethysmograph or low frequency (<100 Hz) phonocardiographpick-up over peripheral artery (e.g., carotid, radial, femoral);

m. Measure the distance from the selected peripheral artery on the bodysurface to the aortic arch (which is at the level of the sternal angleof Louis where the second rib joins the sternum) and enter this distanceinto the computer;

n. Simultaneously record the aortic pulse from the catheter and theperipheral pulse from the plethysmograph or phonocardiograph;

o. Using the ECG for timing, perform fast Fourier transform analysis andreconstruction to correct the aortic pulse signal for phase shift andamplitude;

p. Compute the time difference between the corrected aortic pulse andthe peripheral pulse;

q. Divide the distance between the aortic and peripheral pulses by thetime difference to determine pulse wave velocity;

r. Display the pulse wave velocity on the monitor and record in memory;

s. At a preselected time interval, repeat steps f to r.

Determining Left Ventricular Contractility Index

It is recognized that the contractility index is a sensitive indicatorof cardiac performance. The present apparatus may be used to providesuch an index by computing (dp/dt/MLAP), dp being the diastolic pressureless the mean left atrial pressure, and dt being PEP. To this end, thepatient P is connected to the ECG electrodes as shown in FIG. 1 and toan automatic blood pressure device 22, also as shown in FIG. 1. (Whileuse of an automatic blood pressure device is the preferred manner fordetermining blood pressure, other ways may be used to determine bloodpressure, such as, for example, by arterial pressure transducers.) Afterthe ECG electrodes have been properly connected, the catheter 20 isinserted into the esophagus in accordance with the procedures set forthabove to properly position the left atrial balloon 28.1 behind the leftatrium. With the foregoing equipment attached to the informationprocessing means 12, the frequency of desired measurements is enteredinto the processing means 12. The mean left atrial pressure isdetermined in accordance with the procedure discussed above. The actualpre-ejection time period (PEP) is determined in accordance with theprocedure discussed above, this being equal to "dt" in the equation setforth above. From the blood pressure device, diastolic blood pressure isdetermined, and MIAP is subtracted from diastolic blood pressure to givethe "dp" of the equation set forth above. It is now necessary to onlysolve the equation and to display the result, an approximation of theindex of contractility, on the monitor.

A preferred process for determining a left ventricular contractilityindex includes the following steps:

a. Insert the left atrial balloon behind the left atrium in accordancewith the MLAP process, as illustrated in FIG. 22.

b. Attach skin ECG electrodes.

c. Connect to output of automatic blood pressure device (or arterialpressure transducer) or manually input diastolic pressure.

d. Enter the frequency of desired measurements.

e. Using the MLAP process of FIG. 22, determine the MLAP.

f. Using the STI process of FIG. 23, determine the actual PEP, whichequals dt.

g. From the blood pressure device or manual input, retrieve thediastolic blood pressure.

h. Subtract MLAP from the diastolic blood pressure, thereby obtainingdp.

i. Calculate from the above dp/dt/MLAP.

j. Display the result on the monitor.

k. Repeat steps e to j until the desired number of measurements isreached.

Other Cardiac Performance Determinations

As discussed above, the catheter 20 and its associated pressurizing andmonitoring equipment along with a standard ECG and blood pressure cuffmay be used to inexpensively yet reliably, conveniently, andnoninvasively obtain various cardiac performance parameters. Theapparatus of the present invention may also include a phonocardiographfor use in obtaining systolic time intervals, as previously discussed,and an automatic blood pressure cuff for continuously monitoringsystolic and diastolic blood pressures, which are useful in that thesystolic pressure shows the peak pressure that the ventricle cangenerate while the diastolic pressure is the minimum pressure which theheart has to overcome to cause blood to flow. In addition to aphonocardiograph for the aortic balloon, a phonocardiograph is alsoprovided for the atrial balloon so that the function of the mitral andaortic heart valves may be analyzed with respect to leakage andresistance to flow.

Thus, the noninvasive apparatus of the present invention is provided,without the need for additional pieces of apparatus which may beexpensive or invasive, to inexpensively yet reliably and continuouslyobtain determinations of major cardiac performance parameters asfollows:

mean left atrial pressure to determine the priming pressure of the leftventricle

heart valve function analysis, which addresses a problem in the practiceof anesthesia wherein changes in heart sound or rhythm need to berecognized immediately.

electrographic analysis of the heart's beating frequency and rhythm

systolic time intervals including the ratio PEP/LVET

mean left atrial transmural pressure as an index of left atrial fillingpressure unbiased by thoracic pressure changes such as may be caused,for example, by a mechanical ventilator

systolic and diastolic blood pressures

the left ventricular contractility index

two alternative indices of cardiac output

pulse wave velocity

the determination of pulse amplitude ratios before, during, and afterthe Valsalva maneuver

Esophageal pressure (an established estimate of pulmonary pleuralpressure), which can be used in conjunction with other pulmonarymeasurements to determine (a) the elastic properties of the lungs, (b)lung isovolume pressure-flow curves, (c) the work of breathing, and (d)air stacking or intrinsic positive end expiratory pressure.

The distal and proximal balloons and their spatial relation on thecatheter, as hereinbefore discussed, advantageously allows one standardcatheter to fit virtually all adults and advantageously allows thisstandard catheter to be easily and conveniently positioned just once forreliably obtaining the pressures and sounds in order to determine thevarious cardiac performance parameters listed above.

Statements of theory are contained herein to aid in understanding of theinvention. Although such statements of theory are believed to becorrect, applicant does not wish to be bound by them.

While the best mode of this invention known to applicant at this timehas been shown in the accompanying drawings and described in theaccompanying text, it should be understood that applicant does notintend to be limited to the particular details illustrated in theaccompanying drawings and described above. Thus, it is the desire of theinventor of the present invention that it be clearly understood that theembodiments of the invention, while preferred, can be readily changedand altered by one skilled in the art and that these embodiments are notto be limiting or constraining on the form or benefits of the invention.

What is claimed is:
 1. A method for determining cardiac performance of aperson which may be done noninvasively by paramedical personnel, themethod comprising the following steps: providing an esophageal catheterhaving at least one balloon; inserting into the esophagus of the personthe catheter and positioning the balloon in a position adjacent theaortic arch to sense aortic pressure; pressurizing the balloon; andutilizing effects of aortic pressure on the pressurized balloon whilethe pressurized balloon is adjacent the aortic arch to determine atleast one cardiac performance parameter.
 2. A method according to claim1 wherein the at least one cardiac performance parameter to bedetermined is pulse amplitude ratios before, during, and after aValsalva maneuver, the method further comprising observing pressurechanges in the pressure wave form of the balloon before, during, andafter the Valsalva maneuver is performed.
 3. A method according to claim1 wherein the at least one cardiac performance parameter to bedetermined is an index of cardiac output, the method further comprisesdetermining an area between the aortic pressure wave form and a baselinefor each of a plurality of heartbeats, adding the areas and dividing bythe number of heartbeats to obtain an average, and multiplying theaverage by the heart rate of the person to obtain an index forcomparison with another such index.
 4. A method according to claim 1wherein the at least one cardiac performance parameter to be determinedis pulse wave velocity, the method further comprising obtaining a waveform of a heartbeat by use of the balloon, obtaining the wave form ofthe heartbeat at a position on a peripheral artery, determining the timebetween the onset of the heartbeat on the balloon wave form and theonset of the heartbeat on the peripheral artery wave form, determiningthe distance between the aortic arch and the position on the peripheralartery, and dividing the distance by the time.
 5. A method fordetermining cardiac performance of a person which may be donenoninvasively by paramedical personnel, the method comprising thefollowing steps: providing an esophageal catheter having at least oneballoon; inserting into the esophagus of the person the catheter andpositioning the balloon in a position adjacent the aortic arch to senseaortic pressure; pressurizing the balloon; and utilizing effects ofaortic pressure on the pressurized balloon to determine at least onecardiac performance parameter, the method further comprising selectingthe catheter to also include a second inflatable balloon which is spacedfrom the aortic balloon a distance such that when the second balloon isin a position adjacent the left atrium to sense left atrial pressure theaortic balloon is in a position adjacent the aortic arch to sense aorticpressure.
 6. A method according to claim 5 wherein the step ofpositioning the aortic balloon comprises positioning the second balloonin the position adjacent the left atrium.
 7. A method according to claim6, wherein the step of positioning the second balloon comprisesinflating the second balloon, gradually pulling the catheter up theesophagus while observing pressure wave forms generated by the secondballoon, and, when the pressure wave forms transition from acharacteristic left atrial pressure wave form to a pressure wave formmore characteristic of the pressure wave form of the pulmonary artery oraorta, moving the catheter downwardly about 2 to 3 centimeters until aleft atrial pressure wave form is seen.
 8. A method according to claim5, further comprising selecting the catheter so that the distance isrelated to the distance between the left atrium and aortic arch in mostadult persons.
 9. A method according to claim 5, further comprisingselecting the catheter so that the distance is about 4 centimeters. 10.A method for determining cardiac performance of a person which may bedone noninvasively by paramedical personnel, the method comprising thefollowing steps: providing an esophageal catheter having at least oneballoon; inserting into the esophagus of the person the catheter andpositioning the balloon in a position adjacent the aortic arch to senseaortic pressure; pressurizing the balloon; and utilizing effects ofaortic pressure on the pressurized balloon to determine at least onecardiac performance parameter, wherein the at least one cardiacperformance parameter to be determined is systolic time intervalcomponents, the method further comprising attaching skin ECG electrodesto the patient; determining QS₂ time by determining the time intervalfrom onset of Q from the ECG to the time of the second heart sound froma microphone; determining the left ventricular ejection time from thebeginning of the upslope of the aortic pressure signal from the aorticballoon to the time of the dicrotic notch of the aortic pressure signal;and subtracting the left ventricular ejection time from the QS₂ time todetermine the pre-ejection time period.
 11. Apparatus comprising acatheter including an inflatable balloon adapted for insertion into anesophagus, a source of a gas under pressure, means interconnecting theballoon with the source of a gas under pressure for pressurizing theballoon, means for positioning the balloon within an esophagus in aposition adjacent the aortic arch for sensing aortic pressure, and meansutilizing effects of aortic pressure on the pressurized balloon whilethe pressurized balloon is adjacent the aortic arch for determining atleast one cardiac performance parameter.
 12. Apparatus according toclaim 11, wherein the positioning means comprises a second inflatableballoon on the catheter and adapted for insertion into an esophagus tobe positioned in a position adjacent the left atrium for sensing leftatrial pressure, and means interconnecting the second balloon with thesource of a gas under pressure for pressurizing the second balloon, theballoons spaced apart a distance such that when the second balloon is inthe position adjacent the left atrium to sense left atrial pressure theaortic balloon is in the position adjacent the aortic arch to senseaortic pressure.
 13. Apparatus according to claim 12, wherein saiddistance is related to the distance between the left atrium and aorticarch in most adult persons.
 14. Apparatus according to claim 12, whereinsaid distance is about 4 centimeters.
 15. Apparatus according to claim11 wherein the determining means comprises means utilizing effects ofaortic pressure on the pressurized balloon for analyzing a person'saortic pressure waves before, during, and after a Valsalva maneuver isperformed on the person.
 16. Apparatus according to claim 11 wherein thedetermining means comprises means utilizing effects of aortic pressureon the pressurized balloon for determining an index of cardiac output.17. Apparatus according to claim 11 wherein the determining meanscomprises means utilizing effects of aortic pressure on the pressurizedballoon for determining an index of left ventricular contractility. 18.Apparatus according to claim 11 wherein the determining means comprisesmeans utilizing effects of aortic pressure on the pressurized balloonfor determining pulse wave velocity.
 19. Apparatus comprising a catheterincluding an inflatable balloon adapted for insertion into an esophagus,a source of a gas under pressure, means interconnecting the balloon withthe source of a gas under pressure for pressurizing the balloon, meansfor positioning the balloon within an esophagus in a position adjacentthe aortic arch for sensing aortic pressure, and means utilizing effectsof aortic pressure on the pressurized balloon for determining lengths ofsystolic time intervals.
 20. Apparatus comprising a catheter includingfirst and second inflatable balloons adapted for insertion into anesophagus, a source of a gas under pressure, means interconnecting theballoons with the source of a gas under pressure for inflating theballoons, the balloons spaced apart a distance such that when the secondballoon is in a position adjacent the left atrium to sense left atrialpressure the first balloon is in a position adjacent the aortic arch tosense aortic pressure, and means utilizing effects of at least one ofaortic pressure on the pressurized first balloon while the pressurizedfirst balloon is adjacent the aortic arch and left atrial pressure onthe pressurized second balloon while the pressurized second balloon isadjacent the left atrium for determining at least one cardiacperformance parameter.
 21. Apparatus according to claim 20 wherein saiddistance is related to the distance between the left atrium and aorticarch in most adult persons.
 22. Apparatus according to claim 20 whereinsaid distance is about 4 centimeters.
 23. Apparatus according to claim20 wherein the determining means comprises means utilizing effects of atleast one of left atrial pressure on the second inflated balloon andaortic pressure on the first inflated balloon for analyzing a person'sleft atrial and aortic pressure waves respectively before, during, andafter a Valsalva maneuver is performed on the person.
 24. Apparatusaccording to claim 20 wherein the determining means comprises meansutilizing effects of at least one of left atrial pressure on the secondinflated balloon and aortic pressure on the first inflated balloon fordetermining an index of cardiac output.
 25. Apparatus according to claim20 wherein the determining means comprises means utilizing effects of atleast one of left atrial pressure on the second inflated balloon andaortic pressure on the first inflated balloon for determining an indexof left ventricular contractility.
 26. Apparatus comprising a catheterincluding first and second inflatable balloons adapted for insertioninto an esophagus, a source of a gas under pressure, meansinterconnecting the balloons with the source of a gas under pressure forinflating the balloons, the balloons spaced apart a distance such thatwhen the second balloon is in a position adjacent the left atrium tosense left atrial pressure the first balloon is in a position adjacentthe aortic arch to sense aortic pressure, and means utilizing effects ofat least one of aortic pressure on the pressurized first balloon andleft atrial pressure on the pressurized second balloon for determiningat least one cardiac performance parameter, wherein the catheter is adouble lumen catheter, the apparatus further comprising means includinga bi-polar electrode connected to the catheter above the second balloonfor positioning the second balloon, and a pair of leads extending fromthe electrode for attachment to a ECG and embedded in the material ofwhich the catheter is composed.
 27. A method for determining cardiacperformance parameters of a person on a real-time basis which may bedone noninvasively by health care personnel, the method using anesophageal catheter and associated equipment, the catheter having atleast one balloon, the associated equipment including positioning meanscapable of positioning said balloon, the method being characterized bythe following steps:inserting the catheter into the esophagus of aperson; utilizing the positioning means to position the at least oneballoon adjacent the aortic arch; pressurizing the balloon to couple theballoon to the aortic arch; and using the associated equipment to sensethe pressure in the pressurized balloon to determine at least onecardiac performance parameter.
 28. Apparatus for determining cardiacperformance parameters of a person on a real-time basis which may bedone noninvasively by health care personnel, the apparatus including acatheter including an inflatable balloon adapted for insertion into anesophagus, a source of a gas under pressure, and means interconnectingthe balloon with the source of a gas under pressure for pressurizing theballoon, the apparatus characterized by:positioning means forpositioning the balloon within an esophagus in a position adjacent theaortic arch for coupling the pressurized balloon to the aortic arch; andmeans for sensing the balloon pressure by utilizing the effects of theaortic pressure on the pressurized balloon to determine at least onecardiac performance parameter.